1. Field of the Invention
The present invention relates to cursor control devices and, particularly, to a trackball for single digit control of a wireless terminal.
2. Description of the Related Art
Wireless terminals including cellular telephones and other wireless telecommunication devices are providing increasingly sophisticated functionality. Functions performed by hand-held wireless terminals require an increasing degree of user input and interaction. For example, a typical wireless terminal includes a viewscreen, typically a liquid crystal display (LCD), a keypad, and a plurality of control buttons or switches to allow the user to scroll through menu options on the viewscreen. One such control is a dial which may be used to "roll" through menu options. Alternatively, forward and reverse buttons may be employed to accomplish this task. Finally, certain wireless terminals provide a trackball on the front face of the wireless terminal to position a cursor on the viewscreen. Each of these controls is also associated with a separate select button to allow selection of the menu item highlighted by the cursor.
In ergonomic terms, such menu selection or cursor pointing devices require relatively complex hand or finger movements. More particularly, such user interfaces have typically required the manipulation of a trackball, keys, or dial in order to locate a cursor on the view screen. A separate motion on a separate select key is required to select the item highlighted by the cursor. Frequently this is error-prone and counter-intuitive. Accordingly, there is a need for an improved user interface mechanism for a wireless terminal which is capable of being manipulated by a single finger in both cursor positioning and select modes.
The increasing functionality of wireless terminals also requires the display of increasing amounts of information on the viewscreen. The larger amounts of information generally require larger viewscreens. At the same time, however, the overall size of wireless terminals continues to decrease. Larger viewscreens also facilitate more user-friendly user interfaces, in particular, graphical user interfaces. Accordingly, there is a need for a user interface mechanism that increases the area of a wireless terminal that is available as viewscreen area.
In addition, wireless terminals are subjected to relatively severe operating conditions. Control buttons such as an on-switch may be jostled and thus unintentionally activated. Cursor controls may be exposed to scalding liquids, which can have a deleterious effect on their functionality. This is particularly the case when the control is a trackball, due to the electromechanical or optomechanical structure required to convert the ball's rotation into cursor movement. Accordingly, there is a need for an improved cursor control which is relatively immune from unintentional activation and/or liquid spillage.